1. Field of the Invention
The present invention relates to a drive device for driving a liquid jet head which ejects liquid from nozzle holes to record images and characters on a recording medium, and to a liquid jet head, a liquid jet recording apparatus, and a drive method for the liquid jet head.
2. Description of the Related Art
Generally, a liquid jet head, to which ink (liquid) is supplied from an ink tank, includes a head chip. Ink is ejected from nozzle holes of the head chip onto a recording medium to perform recording. In some liquid droplet ejection type (ink jet type) liquid jet heads (ink jet heads) described above, there is one in which ejection of liquid droplets is performed by driving a piezoelectric actuator provided in the head chip by a head drive portion.
For example, FIG. 9 is a block diagram illustrating a configuration example of a drive portion of a liquid jet head chip which is built into the liquid jet head.
In the example illustrated in FIG. 9, a liquid jet head chip 73 includes 512 nozzles NZ1 to NZ512 (collectively referred to as “nozzle NZ”). A pressure generating element PZT corresponding to each nozzle NZ in the liquid jet head chip 73 is driven by a drive portion 100 mounted on a control circuit board 80. The drive portion 100 includes four driver ICs 101 to 104 as a drive device for the liquid jet head chip 73, and each of the driver ICs (IC1 to IC4) 101 to 104 is configured to drive the pressure generating elements PZT corresponding to the respective 128 nozzles NZ. Further, each of the driver ICs (IC1 to IC4) 101 to 104 inputs, via a connector 100A, image data for printing and various clock signals (shift CLK, pixel CLK, and the like) to be used for printing operation.
Further, FIG. 10 illustrates a configuration example of the drive device for the pressure generating element PZT, and is a block diagram illustrating, for example, a configuration example of the driver IC illustrated in FIG. 9. As illustrated in FIG. 10, the drive device (driver IC) 101 includes a selector 111, a setting value storage element 112, a waveform generating circuit 113, a shift register 121, a latch circuit (latch) 122, a waveform selecting circuit (waveform selection) 123, and a level converting circuit (level conversion) 124. Note that, details of the respective components are described in the section of embodiments below.
The drive device 101 illustrated in FIG. 10 drives, based on drive signals OUT1 to OUTn output from the level converting circuit 124, the pressure generating elements PZT corresponding to the respective n nozzles NZ in the liquid jet head chip 73 (see FIG. 9).
By the way, the drive waveform from the head drive portion, for driving the pressure generating element PZT (piezoelectric actuator), influences the liquid droplet ejection characteristics. For example, the pressure generating element PZT has a very fast response speed with respect to the drive signals OUT1 to OUTn. Therefore, when the pressure generating element PZT is driven by a square wave having a crest value Vp as shown in FIG. 11A, a rapid pressure change occurs inside the nozzle. Therefore, the meniscus motion cannot be controlled with high accuracy, and satellites or mist may be generated. Further, the side wall of the pressure generating element PZT rapidly deforms, and hence cavitation may be generated.
In view of this, as illustrated in FIG. 10 described above, a fixed resistor R is inserted between the level converting circuit 124 and a drive power supply Vd (for example, DC 30 V power supply). In this case, the pressure generating element PZT becomes a capacitive load (capacitor load), and a first order delay circuit is formed between the fixed resistor R and the electrostatic capacitance of the pressure generating element PZT.
Therefore, with the first order delay circuit formed of the fixed resistor R and the electrostatic capacitance of the pressure generating element PZT, as shown in FIG. 11B, the drive voltage for the pressure generating element PZT gently rises up to the voltage Vp while drawing a curved line. Therefore, the drive voltage waveform for the pressure generating element PZT does not rapidly increase, but gently rises from a time t1 to a time t2. Therefore, the deformation of the pressure generating element PZT also becomes gentle, and hence no rapid pressure change occurs inside the nozzle NZ. Thus, generation of cavitation and mist can be prevented.
Further, as for a drive method for the piezoelectric actuator, there is disclosed a technology of controlling the rising and falling shape of the drive waveform to control the liquid droplet ejection characteristics (for example, see Japanese Patent Application Laid-open Nos. 2007-098795 and 2003-276188).
However, Japanese Patent Application Laid-open No. 2007-098795 discloses a technology of providing, as the power supply for supplying power for driving the piezoelectric actuator, a plurality of power supply voltage sources having different output voltages, and selecting the power supply voltages output from the respective power supply voltage sources by a plurality of transistors. When the head drive portion is configured as described above, a plurality of power supply voltage sources need to be prepared, which complicates the circuit and increases the manufacturing cost.
Further, Japanese Patent Application Laid-open No. 2003-276188 discloses a technology in which a plurality of charge resistors having different resistance values are provided for limiting a current value (charge current) for driving the piezoelectric actuator and supplying power for driving the piezoelectric actuator. A plurality of transistors are provided correspondingly to those charge resistors, and a charge resistor which causes a desired current value to flow is selected by the transistors. When the head drive portion is configured as described above, not merely that the circuit configuration is complicated, but also the heat lost increases in the drive circuit forming the head drive portion, and hence the amount of heat generation increases in the head drive portion. Further, a step of trimming the charge resistors or the like is required at the time of manufacture, and hence the manufacturing cost increases.